In refrigeration systems, hot gas bypass lines are used to transfer the discharge gas from the compressor to the low pressure (vacuum line) side of the compressor. Their purpose is to artificially load the compressor upon a drop in pressure load in order to prevent: a drop in evaporator temperature, frosting up of the evaporator coil, operation of the compressor at excessively low back pressures or short cycling of the compressor.
There are a number of methods of bypassing hotgas including: 1) bypassing the gas to the exit of the evaporator section (at a point upstream of the equalizer bulb used for the thermal expansion valve that feeds the gas into the evaporator section from the liquid line); or 2) bypassing the hot gas to the entrance of the evaporator; or 3) simply bypassing the hot gas at a point upstream of the compressor, but downstream of the equalizer bulb mentioned in method 1, this system may be referred to as a close-coupled system.
A close-coupled hot gas bypass system would be desirable over the other by-pass methods since the close coupled system eliminates the large amount of tubing required to bring the gas back to the evaporator. However, these close-coupled bypass systems suffer problems with excessive heating and slugging. Excessive heating of the suction gas (coming from the evaporator to the compressor) can damage the compressor parts. Slugging involves the buildup of liquid in the compressor which also causes damage as the compressor is designed for gas. Prior art teaches that such systems should use an accumulator in the vacuum line to prevent the slugging of oil back to the compressor or to drop the close coupled idea altogether because of the inherent lack of close coupling or to only use this method for a short time.